Coupling Between Br-Hexahelicene Molecules through Br···Br and Br···H Bonds

Non-covalent interactions, particularly halogen–halogen and halogen–hydrogen bonds, play a fundamental role in supramolecular chemistry and are key determinants in the design and stabilization of hierarchical molecular architectures. In this work, we investigate in detail the intermolecular interactions governing the formation and stabilization of a dimer composed of two bromine-substituted hexahelicene (Br-Hexahelicene) molecules, which are inherently chiral helical systems built from six fused aromatic rings.

Geometry optimizations were carried out using the semi-empirical MOPAC method, revealing the presence of two enantiomeric forms, denoted M and P. These enantiomers can self-assemble into energetically equivalent homo-chiral dimers (MM and PP), highlighting the role of molecular chirality in the organization of supramolecular systems. To better understand the origin of stability, an energy decomposition analysis was performed, showing that the dimers are stabilized by a combination of directional short-range interactions and dispersive forces.

In particular, characteristic contacts such as C–Br···Br–C (3.55 Å) and C–Br···H–C (2.97 Å) were identified, together with significant van der Waals contributions. The computed interaction energies (–4.50, –3.33, and –5.44 kcal/mol) clearly indicate that halogen–halogen and halogen–hydrogen bonding interactions constitute the dominant driving forces in the self-assembly process. Additionally, advanced topological and electronic analyses, including the Interaction Region Indicator (IRI), electrostatic potential mapping, and bond-path analysis using Multiwfn, provide a clear visualization and confirmation of the interaction regions, revealing the presence of triangular Br···Br···H binding motifs.

Overall, these results demonstrate the strong propensity of Br-Hexahelicene molecules to form well-organized supramolecular assemblies, emphasizing the crucial role of halogen bonding in the rational design of functional chiral materials with promising applications in nanoscience and surface-based molecular engineering.